Does the light switch on when charging ? What if you plug the orizon to the PC and switch it on ? Does anything happen ?
Get you post a photo of the screen ?
Just a stupid remark, have you tried with another power plug / USB port / cable ? Just in case the problem comes from there, and not the orizon itself. Get an other cable if need be, to make sure of it before you send the orizion back to France.
I woudn't try to open the orizon. I'm afraid you need bookeen support there

Use the contact form there :
http://bookeen.com/fr/supportcontact/